1,3-butadiene, the demand for which is increasing in petrochemical markets, is produced through a naphtha cracking process, a direct n-butene dehydrogenation reaction, or an oxidative n-butene dehydrogenation reaction, and is then supplied to the petrochemical market. Among them, the naphtha cracking process accounts for 90% or more of butadiene supply, but is problematic in that new naphtha cracking centers (NCCs) must be established in order to meet the increasing demand for butadiene, and in that other basic petrochemical raw materials besides butadiene are excessively produced because the naphtha cracking process is not a process for producing only butadiene. Further, the direct dehydrogenation reaction of n-butene is problematic in that it is thermodynamically disadvantageous, and in that high-temperature and low-pressure conditions are required because it is an endothermic reaction, so that the yield is very low, with the result that it is not suitable as a commercial process [L. M. Madeira, M. F. Portela, Catal. Rev., volume 44, page 247 (2002)].
The oxidative dehydrogenation reaction of n-butene, which is a reaction for forming 1,3-butadiene and water by reacting n-butene with oxygen, is advantageous in that stable water is formed as a product, so that the reaction is thermodynamically favorable and the reaction temperature can be lowered. Therefore, a process of producing 1,3-butadiene through the oxidative dehydrogenation reaction of n-butene can be an effective alternative process for producing only butadiene. In particular, when a C4-raffinate-3 mixture or a C4 mixture containing impurities, such as n-butane and the like, is used as the supply source of n-butene, there is an advantage in that excess C4 fractions can be made into high value-added products. Specifically, the C4-raffinate-3 mixture, which is a reactant used in the present invention, is a cheap C4 fraction obtained by separating useful compounds from a C4 mixture produced through naphtha cracking. More specifically, a C4-raffinate-1 mixture is a mixture obtained by separating 1,3-butadiene from a C4 mixture produced through naphtha cracking, a C4-raffinate-2 mixture is a mixture obtained by separating iso-butylene from the C4-raffinate-1 mixture, and a C4-raffinate-3 mixture is a mixture obtained by separating 1-butene from the C4-raffinate-2 mixture. Therefore, the C4-raffinate-3 mixture or C4 mixture mostly includes 2-butene (trans-2-butene and cis-2-butene), n-butane, and 1-butene.
As described above, the oxidative dehydrogenation reaction of n-butene (1-butene, trans-2-butene, cis-2-butene) is a reaction for forming 1,3-butadiene and water by reacting n-butene with oxygen. However, in the oxidative dehydrogenation reaction of n-butene, many side reactions such as complete oxidation etc. are predicted because oxygen is used as a reactant. For this reason, it is very important to develop a catalyst which can suppress these side reactions to the highest degree possible and which has high selectivity for 1,3-butadiene. Examples of catalysts currently used for the oxidative dehydrogenation reaction of n-butene include a ferrite-based catalyst [M. A. Gibson, J. W. Hightower, J. Catal., volume 41, page 420 (1976)/W. R. Cares, J. W. Hightower, J. Catal., volume 23, page 193 (1971)/R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)], a tin-based catalyst [Y. M. Bakshi, R. N. Gur'yanova, A. N. Mal'yan, A. I. Gel'bshtein, Petroleum Chemistry U.S.S.R., volume 7, page 177 (1967)], a bismuth molybdate-based catalyst [A. C. A. M. Bleijenberg, B. C. Lippens, G. C. A. Schuit, J. Catal., volume 4, page 581 (1965)/Ph. A. Batist, B. C. Lippens, G. C. A. Schuit, J. Catal., volume 5, page 55 (1966)/W. J. Linn, A. W. Sleight, J. Catal., volume 41, page 134 (1976)/R. K. Grasselli, Handbook of Heterogeneous Catalysis, volume 5, page 2302 (1997)] and the like.
Among them, the ferrite-based catalyst has a spinel structure of AFe2O4 (A=Zn, Mg, Mn, Co, Cu, and the like). It is known that the ferrite having such a spinel structure can be used a catalyst for an oxidative dehydrogenation reaction through the oxidation and reduction of iron ions and the interaction of oxygen ions and gaseous oxygen in crystals [M. A. Gibson, J. W. Hightower, J. Catal., volume 41, page 420 (1976)/R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)]. The catalytic activities of ferrite-based catalysts are different from each other depending on the kind of metals constituting the bivalent cation sites of the spinel structure. Among them, zinc ferrite, magnesium ferrite and manganese ferrite are known to exhibit good catalytic activity in the oxidative dehydrogenation reaction of n-butene, and, particularly, zinc ferrite is reported to have higher selectivity for 1,3-butadiene than do other metal ferrites [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989)].
It was reported in several patent documents that zinc ferrite-based catalysts were used in the oxidative dehydrogenation reaction of n-butene. Specifically, concerning the production of 1,3-butadiene through the oxidative dehydrogenation reaction of n-butene using pure zinc ferrite made by a coprecipitation method, it was reported that the oxidative dehydrogenation reaction of 2-butene was conducted at 375° C. using a zinc ferrite catalyst having a pure spinel structure, thus obtaining a yield of 41% [R. J. Rennard, W. L. Kehl, J. Catal., volume 21, page 282 (1971)]. Further, it was reported that 1,3-butadiene was obtained at a yield of 21% at 420° C. through an oxidative dehydrogenation reaction, in which 5 mol % of 1-butene was used as a reactant and a zinc ferrite catalyst was used [J. A. Toledo, P. Bosch, M. A. Valenzuela, A. Montoya, N. Nava, J. Mol. Catal. A, volume 125, page 53 (1997)].
Further, methods of manufacturing a zinc ferrite catalyst, by which 1,3-butadiene can be produced in higher yield for a long period of time through pre-treatment and post-treatment conducted in order to increase the activity and lifespan of a zinc ferrite catalyst in an oxidative dehydrogenation reaction, was disclosed in several patent documents [F.-Y. Qiu, L.-T. Weng, E. Sham, P. Ruiz, B. Delmon, Appl. Catal., volume 51, page 235 (1989)/L. J. Crose, L. Bajars, M. Gabliks, U.S. Pat. No. 3,743,683 (1973)/J. R. Baker, U.S. Pat. No. 3,951,869 (1976)].
It was reported in several patent documents that, in addition to the above zinc ferrite catalyst, manganese ferrite-based catalysts were used in the oxidative dehydrogenation reaction of n-butene. Specifically, when 1,3-butadiene is produced through the oxidative dehydrogenation reaction of n-butene using a pure manganese ferrite catalyst made by a coprecipitation method and a physical mixing method, it was reported that 1,3-butadiene was obtained at a yield of 51% at 475° C. through an oxidative dehydrogenation reaction, in which 2-butene was used as a reactant and the manganese ferrite catalyst was used [P. M. Colling, J. C. Dean, U.S. Pat. No. 3,567,793 (1971)/H. E. Manning, U.S. Pat. No. 3,671,606 (1972)].
In the oxidative dehydrogenation of n-butene, the above-mentioned zinc ferrite catalyst is problematic in that metal oxides must be added in order to prevent inactivation, acid treatment must be conducted and complicated post treatment procedures are required; and the manganese ferrite catalyst is problematic in that high temperature must be maintained during coprecipitation in order to produce a manganese ferrite catalyst having a pure spinel structure and the yield of 1,3-butadiene obtained using the manganese ferrite catalyst is lower than that obtained using the zinc ferrite catalyst [refer to H. E. Manning, U.S. Pat. No. 3,671,606 (1972)/T. Kodama, M. Ookubo, S. Miura, Y. Kitayama, Mater. Res. Bull., volume 31, page 1,501 (1996)/Z. J. Zhang, Z. L. Wang, B. C. Chakoumakos, J. S. Yin, J. Am. Chem. Soc., volume 120, page 1,800 (1998)].
The oxidative dehydrogenation reaction of n-butene has another problem in that, when a reactant includes a predetermined quantity or greater of n-butane, the yield of 1,3-butadiene is decreased [L. M. Welch, L. J. Croce, H. F. Christmann, Hydrocarbon Processing, page 131 (1978)]. Therefore, in the above conventional technologies, an oxidative dehydrogenation reaction is conducted using only pure n-butene (1-butene or 2-butene) as a reactant, thus solving such a problem. In practice, reactants containing no n-butane are used even in commercial processes using a ferrite catalyst. As disclosed in the above patent documents, in the catalytic process for preparing 1,3-butadiene from n-butene through an oxidative dehydrogenation reaction, since pure n-butene is used as a reactant, an additional process of separating pure n-butene from a C4 mixture is required, thus inevitably decreasing economic efficiency.